Mainframe+Blog
Mainframe+Blog
  • What is the difference between a schema and a sub schema?

The schema is the physical arrangement of the data as it appears in the DBMS. The subschema is the logical view of the data as it appears to the application program.

  • What is a region?

Region is used synonymously with area. It is group of logically contiguous pages.

  • What is a page?

A page is a smallest unit of storage in an IDMS database.

  • Explain the difference between record occurrence and record type?

A record occurrence is the instance of the record; it is the smallest addressable unit of data. A record type is the description of record; there needn’t be any occurrences.

  • What is difference between the local and central version operating modes?

In local there is no IDMS system running above the DBMS. It’s the most efficient mode but lacks the recovery and integrity facility of the central version (CV) control program. In CV many application programs access the database through the single copy of the DBMS.

  • What is a run unit?

A run unit is a logical unit of work; it is analogous to a CICS task.

  • What is an OOK-Rec?

An OOK-Rec is one of a kind record set, used to get to another record set

  • What is a junction record?

A junction record is a member record type that allows for many-to-many relationship between its two owner records. For a school database CLASS record is a junction for the TEACHER and SUBJECT record types.

  • Name and explain the three location modes.

CALC is based on symbolic value, which is used to determine the target page. VIA modes is for members only. VIA records are stored near their owners. In DIRECT mode the target is specified by the user and is stored as close as possible to that page.

  • What is a set? What pointers are required, what are possible? How many sets be ordered?

A set is an owner record and, optionally, its member record. There are three types of pointers         next, prior and owner, but only next is required. There are five possible orders for arrangement of sets; first – insert at beginning, last – insert at end of set, next – insert after current of set, prior to current of set and sorted  – insert according to sort value.

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